As one of methods for achieving an increase in speed of communication, there is a method in which a transfer data amount is reduced. The method in which a transfer data amount is reduced is effective for low-band channels because a used band can be reduced. Examples of the method in which a transfer data amount is reduced include a method in which data transmitted in duplicate is removed and a method in which data for transmission is compressed.
In the method in which data transmitted in duplicate is removed, for example, a system configuration in which a transmission-side apparatus and a reception-side apparatus are placed in a transmission-side network and a reception-side network, respectively, is often employed. The transmission-side apparatus and the reception-side apparatus each cache previously-processed data in advance, and the transmission-side apparatus checks if there is duplication of data for transmission, using cached data, and if there is duplication of data for transmission, transmits outline information on the data for transmission instead of the data for transmission. Upon reception of the outline information on the data, the reception-side apparatus reads the data from the cache and transfers the data to a destination. Since the outline information on the data for transmission is small in size compared to the data for transmission, the amount of data transferred can be reduced, enabling reduction of a band used between the transmission-side apparatus and the reception-side apparatus.